BobCo19-65- if repeated use is such a problem with graphite arrows, how is it that fishing rods can be flexed millions of times and still function perfectly?

And spine testers don' t really " test" the spine- they just find it and see if it' s unusually severe...

Sorry, I have no idea what you are talking about. Maybe you could explain this a little.


Spine is basically a measure of the stiffness of an arrow shaft. It measures the deflection a shaft when a two pound weight is suspended from the middle of the shaft when the shaft is supported at two points 26 inches apart.

Technically, it' s not really

What you are describing is Flex. Spine is actually a characteristic imparted via the manufacturing process that runs the length of the shaft, where it is most resistant to flex. Think of it as a kind of back bone.

Arrow makers always say spine, but what they are really talking about is flex. Can flex be affected by spine? Absolutely. Are spine and flex the same? No.

I think the intermingling of these two distinct terms is what is causing the confusion in the two threads going on about spine now...

Yep! Took me a spell, but that' s about what I' ve figured out too. Differences in terminology.

My spine (flex) tester is a couple of 1X6' s. One as a back and the other as a base, with 1X2' s mounted upright, 26" apart, with ' V' notches cut in the ends to hold the arrow shaft. I' ve got an arm made from flat steel loosely bolted to the back with a large bolt at the other end of the arm holding enough washers to make up 2 pounds of weight. The length of the arm is such that the weight will fall in the center of the shaft when it' s on the supports. A 1" travel indicator that measures to .001" is mounted to the base directly under the wieght and centered with the arrow shaft.

I don' t have it all worked out to where it will give exact spine, but it does great for checking variances between one shaft and another. Or variances around the same shaft.

Actually, at 26" between centers, mine is set up for wood arrows. For carbon arrows the supports should be 28" apart.

Oh, we are being technical. (Kidding) .


Isn' t what you are describing " flex" and what I am describing, the same as static spine???? If not, please explain. I am in no means an expert on this.

Aaaaahhhhh.... You are right, we are talking about two different things completely. My mistake. That' s interesting...

So when you measure " spine" as you call it, do you rotate the arrow 360 degrees while under load and use the stiffest axis as a measure, or ??

Neither am I...

I' m pretty certain static spine refers to the spine in an arrow at rest with no outside influence exerted upon it.

Take golf shafts for instance. Finding the ideal Flex for one' s individual swing is paramount to good repeatable performance. However, spine aligning is the popular rage right now as current technology doesn' t quite allow one to build a shaft without a spine. So, builders align the club head and grip along the " spine" , so it influences flex the same way club to club, hopefully. From there, they vary the flex of the shaft to meet one' s swing speed and dynamic loading of the shaft. Some manufacturers are very close to producing a spineless shaft (like Apache), where the shaft will flex identically no matter how it' s held, but the majority don' t/can' t, apparently.

This get' s into what Arthur was saying, he aligns his cock feathers along the spine, to have the best potential for repeated flex from arrow to arrow within a batch. As long as the shafts flex identically, he should be good to go. If they don' t, he' ll get fliers. Matching flex, particularly if using a fixed rest, is tantamount to tight grouping.

After all of this, I' m pretty certain everyone is right Spine doesn' t move or degrade, but arrow flex changes due to extended use or repeated heavy impact, causing fliers and bad arrows.

excert of articale on static spine

[quote][Try bending a sheet of paper - it' s easy. Roll the paper into a tube and try bending it again - it' s a lot harder. How easy it is to bend a sheet of paper or an arrow shaft depends on its stiffness. The accepted (Easton derived) standard for the stiffness of an arrow shaft is its static spine. The shaft is supported at two points a specified distance apart and a specified weight hung at the mid point. The amount the mid point of the shaft drops from the horizontal determines the shaft spine. The lower the stiffness of the shaft the more it sags and the larger the measured deflection. Given the support spacing and the weight hung the static spine depends on the elasticity of the shaft material(s) and the materials' geometries.
/quote]


Here is the article.

http://homepage.ntlworld.com/joetapley/spine.htm

But see, they are still measuring ' flex.' Aluminum arrows don' t really have much of a ' spine' because they flex pretty much the same no matter where you rotate the shaft to check the flex. On woods and carbons, there are pretty hefty differences from one point around the shaft to the next. Where the stiffest line running lengthwise along the shaft is, that' s the actual spine of the shaft.

Our use of the term ' spine' to describe ' flex' is a holdover from wood arrow days. The spine of a wood arrow runs with the grain and that is where you test the flex. We archers just came to call it spine. Incorrectly, I might add.

Patapsco. Yes, that' s exactly what I do since I learned that carbons have such a wide variance in flex, especially when you get off the actual spine.